Discovery I left front (driver) window won't go down

I have a 1996 Disco 1, 158,000 miles. The driver's window will go up but not down. I replaced the regulator because the plastic washer had failed, this restored the up function. I tried the switch from the right front window, which works, and still no going down. I checked the ECB board, and it looks ok, I previously had re-soldered it to restore rear window function several years ago. So any thoughts on what is wrong now? How to diagnose it from here?